The present invention generally relates to intravascular balloon catheters. The present invention is particularly suited, but not limited, for application to intravascular stent delivery catheters.
Angioplasty procedures have gained wide acceptance in recent years as an effective and safe method for treating various types of vascular disease, particularly vascular restrictions or stenoses that inhibit the flow of blood through arterial vasculature. Angioplasty procedures may be performed in virtually any part of the vascular system including the peripheral vasculature, coronary vasculature, and cerebral vasculature. The most common form of angioplasty utilizes a dilatation catheter that includes an inflatable balloon at its distal end. The catheter is percutaneously inserted into the patient""s vascular system and is navigated through the vasculature to the treatment site. Typically, the treating physician utilizes an x-ray fluoroscope to guide the dilatation catheter through the vasculature and position the inflatable balloon across the restriction. Once in position, the balloon is inflated utilizing a pressure source to cause the balloon to engage and dilate the restriction, thus increasing its inside diameter and reestablishing acceptable blood flow therethrough.
Although angioplasty procedures are typically initially successful, a significant number of vascular restrictions reappear. The reappearance of a vascular restriction may be due to elastic recoil or reformation of the stenosis by smooth muscle cell proliferation (i.e., restenosis). To address this issue, treating physicians often utilize an intravascular stent to maintain the patency of the dilated restriction. A stent typically comprises a tubular structure that mechanically engages the interior wall of the vessel to maintain the inside diameter of the vessel after dilatation. The stent reduces the tendency of the vascular wall to elastically recoil after dilatation. Although some smooth muscle cell proliferation occurs around the stent to essentially embed the stent in the vascular wall, the gross dilated diameter is maintained. In this manner, the stent maintains the patency of the dilated restriction thereby maintaining adequate blood flow therethrough.
A number of stent delivery systems have been developed, typically comprising a balloon catheter having the stent mounted on the balloon. Such a deliver system may be utilized to deliver and deploy a balloon-expandable stent or a self-expanding stent. A self-expanding stent expands from its initial profile delivery diameter to its final deployed diameter by virtue of elastic forces contained in the stent structure. The balloon is then used to tack up or firmly engage the stent against the vessel wall. A balloon-expandable stent, by contrast, expands from its initial profile delivery diameter to its final deployed diameter by virtue of forces applied by the expandable balloon.
With both types of delivery systems, the stent delivery catheter is positioned such that the balloon and the stent loaded thereon extend across the dilated restriction. Once in position, the stent is deployed by either pulling back a retaining sleeve as with a self-expanding stent or by inflating the balloon as with a balloon-expandable stent. In this manner, the stent is positioned across the dilated restriction to maintain adequate blood flow therethrough.
Balloon-expandable stents have a tendency to migrate distally during deployment. The tendency of the balloon-expandable stent to migrate distally during deployment is due in part to the non-uniform inflation of the balloon. In particular, as pressurized fluid enters the balloon, the proximal end of the balloon begins to expand first. As the proximal end of the balloon expands, a longitudinal force is applied to the stent in addition to a radial force. If the longitudinal force exceeds the frictional force between the stent and the balloon surface, the stent will migrate distally. This may result in the stent being deployed in an undesirable location such as a position distal to the dilated restriction. Once the balloon-expandable stent has been deployed, it is difficult, if not impossible, to change its location. Accordingly, it is desirable to deploy the stent accurately by reducing the tendency of the balloon-expandable stent to migrate distally.
The present invention overcomes these disadvantages by providing an intravascular balloon catheter that inflates the balloon more effectively, which is particularly useful for stent delivery. For example, the balloon catheter of the present invention may be configured to inflate the balloon uniformly such that a stent loaded on the balloon will not have a tendency to migrate during deployment. Alternatively, the balloon catheter of the present invention may be configured to initially inflate the distal end of the balloon to prevent distal migration.
One embodiment of the present invention provides an intravascular balloon catheter that includes a catheter shaft and a balloon, wherein the proximal end of the balloon is connected to the distal end of the shaft. A tip is disposed in the interior of the balloon with the proximal end of the tip extending from the distal end of the catheter shaft and the distal end of the tip connected to the distal end of the balloon. The tip includes a fluid path to facilitate the passage of inflation fluid from the inflation lumen to the interior of the balloon, and the tip may further include a guide wire lumen extending therethrough. The fluid path may be configured to inflate the balloon uniformly or to initially inflate the distal end of the balloon. The fluid path may be defined by channel(s) in the tip, groove(s) in the tip, or by utilizing a tip having a non-circular profile.